Legendary director Steven Spielberg is "saddened" by Sam Neill's death ... and he has nothing but good things to say about his classic "Jurassic Park" lead.

In a statement to multiple outlets, Steven says ... "I owe a debt of gratitude to Roger Donaldson, Gilliam Armstrong, Graham Baker and Phillip Noyce for casting Sam Neill in the roles in which he was so brilliant that brought him to my attention and led to his playing Dr. Alan Grant in Jurassic Park."

The director also says, "Sam was exceptionally collaborative. It was a stretch for him to play a character who acted as though children were messy and smelly because this was the opposite of the loving father he was to his children."

Steven says he "adored" working with Sam on the 'Jurassic' franchise and says he will never be forgotten.

As we reported ... Sam died on Monday, just months after he announced his recovery from a rare and aggressive blood cancer.

Sam was 78.